1. Field of the Invention
The present invention generally relates to a sensor for sensing objects in proximity to a vehicle, and more particularly to an electronically scanning radar sensor which is especially advantageous for scanning around a corner of a vehicle.
2. Description of the Related Art
Phased array radar systems are effective for scanning areas to sense the presence of objects therein. However, such systems have been heretofore very expensive, and limited to military applications in which cost is not a particular problem. Applications of conformal radar antenna arrays for mounting on aircraft, missiles, satellites, etc., are described in chapter 21 of a textbook entitled "Antenna Engineering Handbook", edited by R. Johnson et al, McGraw Hill, New York (1984). This textbook also includes a general description of microstrip antennas in chapter 7, and phased arrays including Butler and Blass matrices in chapter 20, as component elements of phased array radar systems.
A major obstacle to adapting phased array radar sensors to civilian applications such as near-object detectors (NOD) for automotive vehicles has been the complexity of the phased arrays which interconnect the transceiver to the antenna elements. Waveguides have been conventionally used for this application, as described in U.S. Pat. No. 4,812,788, entitled "WAVEGUIDE MATRIX INCLUDING IN-PLANE CROSSOVER", issued Mar. 14, 1989, to M. Wong et al. This patent discloses an improved configuration which enables the waveguides to be formed in a single plane without crossovers. However, the manufacturing process requires precisely forming the waveguides, walls separating the waveguides, coupling apertures, and phase shifters in a parallel array within a common metallic plate using automated milling machines. This process is very time consuming and expensive, and generally precludes application to commercial use.